The invention relates to an injection and mixture formation process as well as apparatus to implement same for air-compressing internal combustion engines provided in the piston crown with a rotation-symmetrical combustion chamber in which the air for combustion to be inducted is imparted a rotation about the longitudinal axis of the combustion chamber and the fuel is injected by a fuel injector arranged in the region of the combustion chamber rim in the cylinder head at an angle relative to the longitudinal axis of the combustion chamber and substantially in the direction of the rotating air for combustion.
In the case of air-compressing, direct-injection internal combustion engines, a number of injection and mixture formation processes as well as suitable equipment have been developed in the course of many years which, however, all have lesser or greater merits and demerits. Many of these processes were abandoned after a short while on account of great disadvantages so that only a few classical injection processes are looked upon as trend-setting by today's engineering world.
One of these concepts, for instance, provides for the fuel to be injected through a nozzle arranged centrally or substantially centrally relative to the combustion chamber opening in the form of a plurality, or at least three, sprays radially outwards into the air for combustion contained in the combustion chamber. This air for combustion has no, or nearly no, controlled swirl flow imparted to it on entering, turbulence being produced only by the squish effect, mainly in constricted or even omega-shaped combustion chambers. Multi-spray injection into this squish turbulence results in a more or less good mixture preparation and, consequently, combustion under uncontrolled flow conditions. It must be looked upon as a further disvantage that, after initial ignition, spontaneous, rough and noisy combustion occurs because there are many fuel particles which, on account of the short time they have spent in the compressed air, have not yet been sufficiently heated and/or evaporated. Generally, the rates of pressure rise d.sub.p measured in internal combustion engines of this type at full load range from 6 to 8 bar per degree crank angle. In the part-load range, the ratio d.sub.p /d .alpha. is even greater or at least equal to 8 bar/.degree. crank angle which leads to the well-known phenomenon of Diesel pinking.
The engines have only medium loadability at the smoke limit, fuel economy is moderate because relatively high flow losses occur and fuel preparation is not at an optimum. At low loads and/or speeds as well as during starting, the fuel tends to impinge on the combustion chamber wall almost perpendicularly because of the short trajectories of the fuel whereby gases are formed which have an unpleasant odour and cause irritation of the eyes. There is a high emission level of unburnt hydrocarbons (Swiss Patent Specification 175 433).
Another injection process known provides for a comparatively moderate rotary motion about the longitudinal axis of the combustion chamber to be imparted to the air for combustion flowing into the combustion chamber. Fuel injection is also by means of a plurality of sprays which extend across the air flow radially outwards from a nozzle arranged centrally relative to the combustion chamber. The combustion chamber is mostly formed with a shallow shape and has hardly any constriction at the combustion chamber rim.
After initial ignition, there is also a spontaneous, rough and noisy combustion in this type of engine, because too large an amount of ignitable mixture already exists in the combustion chamber at the time of ignition. Generally, the rates of pressure rise are similar to the first-described process, viz EQU d.sub.p /d.alpha.=6 to 8 bar/.degree. crank angle in the full load range and EQU d.sub.p /d.alpha.&gt;8 bar/.degree. crank angle at part load,
so that the problem of Diesel pinking is again not overcome. Admittedly, loadability at the smoke limit is relatively good because the process allows more intensive controlled mixing of the fuel and air for combuction. Fuel efficiency and fuel economy can also be described as good because only small total flow losses occur thanks to the generation of the air swirl and the small squish flow losses at the combustion chamber rim. Heat transfer losses at the combustion chamber wall, too, as a result of the comparatively low air swirl have to be considered to be low. During operation in the low load and/or speed range as well as during starting, the same kind of drawbacks occur, however, as in the previously described process.
Also known from the German Patent Specification 964 647 or the German Patent Specification 969 826 is an internal combustion engine where the piston crown is formed with a combustion chamber in the shape of a solid of rotation with a constricted throat into which fuel is injected at an angle by a nozzle arranged laterally at the combustion chamber rim. There is no controlled air flow provided and squish flow and atomization by the nozzle are relied upon for the mixing of the fuel with the air for combustion, therefore, the same drawbacks occur as described above.
Finally, the injection and mixture formation processes to be distinguished in general include the process of wall deposition of the fuel (German Patent Specification 865 683). This process preferably uses a spherically shaped combustion chamber with a constricted combustion chamber rim and the fuel is applied by a nozzle located off-centre relative to the combustion chamber by one or more sprays onto the combustion chamber wall where it is spread as a thin film by the kinetic energy and by the air swirl prevailing in the combustion chamber. In particular due to the hot combustion chamber wall, it is evaporated and then intimately mixed with the air for combustion.
After initial ignition, continuous evaporation of additional fuel from the wall results in a smooth and low-noise combustion which is borne out by the fact alone that a value of d.sub.p /d.alpha.=3 to 4 bar/degree crank angle is obtained at full load. At part load, this value is even lower so that pinking is prevented from occurring.
The intensive mixture formation permits good loadability at the smoke limit and high fuel efficiency, but there is a penalty of higher flow losses due to the high air swirl (50% higher than in direct-injection internal combustion engines) and due to the squish turbulence at the combustion chamber rim. Furthermore, the high-intensity air swirl results in high thermal losses to the combustion chamber wall, especially in the area of the constricted throat whereby the latter and also the cylinder head are subjected to high thermal stresses.
In the low load and/or speed range as well as during starting when the combustion chamber wall is still cold or relatively cold, the fuel deposited on the wall can only insufficiently be evaporated which results in incomplete combustion with unpleasantly smelling exhaust gases forming and the emission of unburnt hydrocarbons. The adoption of a longer free trajectory of the fuel as proposed by the German Patent Specification 20 38 048 failed to overcome the drawbacks completely.